There are a variety of tanks available for storing various substances both belowground and aboveground. Existing underground tanks suffer from many drawbacks, some of which render such tanks unusable as a result of more stringent modern day environmental guidelines and requirements. One drawback is that underground tanks tend to leak their contents, whether through corrosion or other causes such as breaks due to ground movements. Leaks are typically very difficult to detect, and, once detected, it is virtually impossible to tell how long the leak has been present. Such tanks not only require expensive excavation to install, but require further excavation for removal, repair or replacement. Underground tanks are usually replaced rather than repaired due to impacts and damage during excavation and repair. Reclaiming a contaminated site is also very time consuming and expensive. Underground tanks used in the petroleum industry further require berms and dykes which claim a large surface area at well sites, and make access to the tank more difficult. Removing product from such tanks is expensive due to required use of vacuum trucks rather than less expensive pump trucks.
Aboveground tanks, on the other hand, avoid some of these problems. They do not require excavation, for instance, but may require berms depending on whether the tank is single or double walled. Existing aboveground designs have their own drawbacks, particularly in extreme cold (or hot) climates. Keeping stored liquid from freezing and damaging the tank usually requires more than just thermal insulation but a heating system of some sort. A disadvantage of prior art systems is that they focus on heating the liquid itself, which can be expensive and impractical. Hence, usage of aboveground tanks in such extreme climates is not as popular as it should be, even though from an environmental standpoint, leak detection is much easier and quicker to detect than in underground tanks.
What is desired therefore is a novel aboveground tank assembly for storing liquid substances which overcomes the limitations and problems of these prior art tanks. Preferably it should provide a dual containment assembly where a sizeable air space between an inner tank for receiving and storing the liquid and outer tank is provided to trap any leakage from the inner tank. A means for readily detecting any leak should be provided, and a shut-off mechanism should be available to stop liquid flow and prevent overflow of the inner tank. Preferably the novel tank should have another air space beneath the outer tank communicating with the first air space, and a heater for heating these air spaces whereby the stored liquid is prevented from freezing by the surrounding air spaces rather than direct heating of the liquid. An air exchange assembly should provide for air communication between air spaces, yet prevent any leaked liquid in the first air space from entering the second air space. The assembly should be enveloped and effectively isolated from the ambient by an insulating layer. The assembly should further provide for storage of more than one type of liquid, and for a means of at least partially separating solids from the liquid. It should also provide a vent for the inner tank which reclaims at least some moisture from vented gases and returns the moisture to the assembly.
In a preferred aspect the present invention provides an aboveground containment assembly for storing liquids comprising:
an inner tank for receiving and storing said liquids; PA1 an outer tank surrounding said inner tank and forming a first air space therebetween for trapping any of said liquids which might escape said inner tank; PA1 a support means beneath said outer tank for providing a second air space between the outer tank and a ground support surface; PA1 an insulating layer for substantially isolating said inner tank, outer tank and support means from the ambient; PA1 a vapour exhaust means for said inner tank; PA1 pipe means for liquid communication between said inner tank and external liquid sources for filling and emptying said inner tank; PA1 measurement means for measuring the amount of liquid in said inner tank and including a shut-off mechanism for stopping the flow of liquid through said pipe means to said inner tank upon said liquid reaching a pre-set level therein; and PA1 a detector accessing said first air space for detecting liquid leakage from said inner tank. PA1 an outer tank located aboveground; PA1 an upper inner tank for primary liquid storage located within said outer tank so as to form a first air space therebetween for containing any egress of liquid from said upper tank; PA1 a sub-floor assembly beneath said outer tank for elevating and supporting a base of said outer tank aboveground and to form a second air space beneath said outer tank base; PA1 an external insulating layer for substantially isolating said upper inner tank, outer tank and sub-floor assembly from the ambient; PA1 a vapour and pressure exhaust means for said upper inner tank; PA1 inlet and outlet pipe means for filling and emptying said upper inner tank; PA1 measurement means for measuring the amount of liquid in said upper inner tank and including a shut-off mechanism for interrupting the flow of liquid through said pipe means upon said liquid reaching a pre-set level within said upper inner tank; and PA1 a detector accessing said first air space for detecting liquid therein.
In another aspect the invention provides a containment assembly for liquid storage comprising: